The present invention relates generally to ink-jet printing ink compositions having superior smearfastness, as compared to prior art ink-jet ink printing compositions, and, more particularly, to the use of core/shell and other polymers, or binders, with hydrophobic and hydrophilic portions that contribute to such superior smearfastness and additives to the inks that improve their print reliability.
Core/shell polymers are well-known; such polymers typically have a hydrophilic portion and a hydrophobic portion comprising a latex particle morphology consisting of an inner xe2x80x9ccorexe2x80x9d,surrounded by an outer xe2x80x9cshellxe2x80x9d. Core/shell polymers are commonly used to disperse molecules or particles, such as pigments, which are ordinarily insoluble in water, but which, after association with the core/shell polymer, form stable dispersions in water. Dispersion occurs when the hydrophobic portion of the polymer associates with the water-insoluble molecule or particle, and the hydrophilic portion of the polymer disperses with water.
U.S. Pat. No. 4,597,794 discloses the dispersion of pigments in an aqueous vehicle, using aqueous binders comprising both hydrophilic and hydrophobic components. The dispersion of the pigment is followed by centrifugation to eliminate the nondispersed components such as agglomerates. Examples of the hydrophilic component comprise polymers of monomers having a mainly additively polymerizable vinyl group, into which hydrophilic construction portions such as carboxylic acid groups, sulfonic acid groups, sulfate groups, etc. are introduced by using a predetermined amount of an xcex1,xcex2-unsaturated monomer such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid, fumaric acid monoester, vinyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, sulfonated vinylnaphthalene, etc. Examples of the hydrophobic portion comprise polymers of monomers selected from the group consisting of styrene, styrene derivatives, vinylnaphthalene, vinylnaphthalene derivatives, and xcex1,xcex2-ethylenic unsaturated carboxylate of aliphatic alcohol having C8-C18. In addition to the foregoing monomers, also included are acrylonitrile, vinylidene chloride, xcex1,xcex2-ethylenic unsaturated carboxylate, vinyl acetate, vinyl chloride, acrylamide, methacrylamide, hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate, N-methylol acrylamide, N-butoxymethyl acrylamide, etc.
U.S. Pat. No. 5,082,757 discloses encapsulated toner compositions comprising a core and a hydroxylated polyurethane microcapsule shell derived from the polycondensation of a polyisocyanate and a water soluble carbohydrate. The core comprises a polymer binder, pigment, dye, or mixtures thereof. Examples of the polymer binder include polymerized monomers selected from the group consisting of acrylates, methacrylates, and olefins including styrene and its derivatives.
U.S. Pat. No. 5,461,125 discloses waterborne core-shell latex polymers useful as adhesive films, rather than super-dispersion stability. The core comprises a (co)polymer comprising a (meth)acrylate ester, while the shell comprises a copolymer, the copolymer comprising (1) a nitrogen-bearing ethylenically-unsaturated free-radically polymerizable monomer, (2) at least one (meth)acrylate ester of about a C1 to C14 alcohol, and (3) an optional ethylenically-unsaturated free-radically polymerizable silane monomer, wherein the nitrogen-bearing ethylenically-unsaturated free-radically polymerizable monomer comprises about 15 to 60 wt % of the shell and wherein the core comprises about 40 to 85 wt % of the weight of the total core-shell latex particle. The polymers obtained by practicing the teachings of the disclosure have molecular weights of 400,000 or more, and the total low Tg component (less than xe2x88x9210xc2x0 C.), where Tg is the glass transition temperature, is greater than 60 wt %.
U.S. Pat. No. 5,656,071 discloses ink compositions useful for ink-jet applications. These compositions include an insoluble pigment and a polymeric dispersant. In one embodiment, the polymeric dispersant comprises block or graft copolymers comprising a hydrophilic polymeric segment (particularly an acrylate or methacrylate copolymer) and a hydrophobic polymeric segment which includes a hydrolytically stable siloxyl substituent.
Heretofore, ink-jet printers have not had printing performance and durable print properties of competitive printer technologies. The foregoing cited patents do not provide for useful, durable film-forming properties upon removal of the water or solvent. Film durability includes wet and dry rub resistance, highlighter smearfastness, lightfastness, and waterfastness (e.g., hot and cold water, under spill, soak, and rub conditions).
In particular, formulating an ink-jet ink often involves compromising competing interests. For example, it is possible to enhance one property, such as durable film-forming of the colorant. However, such enhancement usually results in the degradation of another property, such as printing stability associated in thermal ink-jet with resistor fouling or nozzle clogging (kogation or decapxe2x80x94nozzle crusting).
Many thermal ink-jet inks exhibit poor smearfastness due to the aqueous solubility of the colorant and/or the dispersibility of the colorant. Efforts continue to develop ink-jet printing ink compositions that evidence the level of smearfastness that a water-insoluble colorant, such as a pigment, possesses, while retaining other desirable printing characteristics.
In accordance with the invention, specific core-shell binders and certain additives for use in ink-jet printing ink compositions are provided. The specific core/shell binders have the general formula (I)
[(A)m(B)n(C)p(D)q(E)r]xxe2x80x83xe2x80x83(I)
wherein A, B, C, D, and E represent functionalities as follows:
A=at least one hydrophobic component contributing to improved durable, film-forming properties selected from moieties which, when homopolymerized to a solid state, have a glass transition temperature (Tg) in the range between xe2x88x92150xc2x0 and +25xc2x0 C.;
B=at least one hydrophobic and solvent barrier moiety used to adjust the Tg of the hydrophobic component of the polymer (I) which, when homopolymerized to a solid state, has a Tg greater than +25xc2x0 C.;
C=at least one hydrophilic component, selected from a wide variety of water-soluble monomers (optional);
D=at least one UV absorber (optional);
E=a moiety having at least one highly polar functional group (optional);
m=10 to 30 wt %;
n=40 to 90 wt %;
p=0 to 30 wt %;
q=0 to 50 wt %;
r=0 to 40 wt %;
m+n+p+q+r=100 wt %; and
x=1 to 100,000,
with the proviso that at least one of C and E must be present.
The molecular weight (weight average) of polymer (I) is between about 1,000 and 2,000,000.
The polymers useful in the practice of the invention are prepared by emulsifying the monomers and then conducting a free-radical polymerization in water.
The additives employed in the practice of the present invention include water-soluble or water-dispersive amines, polyamines, polyalcohols, amine alcohols, polyesters, and organic acids.
In the present invention,
(a) water-soluble and/or water-dispersive amines and polyamines are found to be good stabilizers for anionic dispersive components, including emulsion polymers (primer, durable polymer, etc.), colorants (pigments, dyes, etc.); and
(b) water-soluble and/or water-dispersive acids and polymeric acids are found to be good stabilizers for cationic dispersive components, including emulsion polymers (primer, durable polymer, etc.), colorants (pigments, dyes, etc.).
It has also been found in the present invention,
(c) in the case of inks employing anionic dispersive components (colorants, emulsion polymers, etc.), a combination of a suitable quantity of polymeric acid with a suitable amount of amines can further improve the print performance; and
(d) in the case of inks employing cationic dispersive components (colorants, emulsion polymers, etc.), a combination of a suitable quantity of polyamines with a suitable amount of acids can further improve the print performance.
It has further been found in the present invention,
(e) the non-ionic water-soluble or water-dispersive polyalcohols and polyesters can improve the print performance of the ink comprising either cationic, anionic, and non-ionic dispersive components (colorants, emulsion polymers, etc.).
The amine alcohols have the general formula (II) 
where R1 and R2 are independently selected from the group consisting of hydrogen, alkyl, alkoxy, aryl, and phenoxy, R is alkyl, and X is selected from the group consisting of hydrogen, alkyl, aryl, xe2x80x94OH, xe2x80x94COOH, and xe2x80x94CHO.
Alternatively, organic acids, whether water-soluble or water-insoluble, are employed in conjunction with the binder polymer in formulating the smear-fast inks of the present invention. The organic acids include polymeric acids as a sub-class.
The ink formulation of the present invention comprises:
5 to 50 wt % water-miscible solvent;
0.5 to 10 wt % colorant;
0.1 to 10 wt % core/shell polymeric binder;
0.005 to 50 wt % additive; and
water.